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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="intrusive.safe_hook"></a><a class="link" href="safe_hook.html" title="Safe hooks">Safe hooks</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="safe_hook.html#intrusive.safe_hook.features">Features of the safe mode</a></span></dt>
<dt><span class="section"><a href="safe_hook.html#intrusive.safe_hook.configuring">Configuring safe-mode
      assertions</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="intrusive.safe_hook.features"></a><a class="link" href="safe_hook.html#intrusive.safe_hook.features" title="Features of the safe mode">Features of the safe mode</a>
</h3></div></div></div>
<p>
        <span class="bold"><strong>Boost.Intrusive</strong></span> hooks can be configured
        to operate in safe-link mode. The safe mode is activated by default, but
        it can be also explicitly activated:
      </p>
<pre class="programlisting"><span class="comment">//Configuring the safe mode explicitly</span>
<span class="keyword">class</span> <span class="identifier">Foo</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">list_base_hook</span><span class="special">&lt;</span> <span class="identifier">link_mode</span><span class="special">&lt;</span><span class="identifier">safe_link</span><span class="special">&gt;</span> <span class="special">&gt;</span>
<span class="special">{};</span>
</pre>
<p>
        With the safe mode the user can detect if the object is actually inserted
        in a container without any external reference. Let's review the basic features
        of the safe mode:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            Hook's constructor puts the hook in a well-known default state.
          </li>
<li class="listitem">
            Hook's destructor checks if the hook is in the well-known default state.
            If not, an assertion is raised.
          </li>
<li class="listitem">
            Every time an object is inserted in the intrusive container, the container
            checks if the hook is in the well-known default state. If not, an assertion
            is raised.
          </li>
<li class="listitem">
            Every time an object is being erased from the intrusive container, the
            container puts the erased object in the well-known default state.
          </li>
</ul></div>
<p>
        With these features, without any external reference the user can know if
        the object has been inserted in a container by calling the <code class="computeroutput"><span class="identifier">is_linked</span><span class="special">()</span></code>
        member function. If the object is not actually inserted in a container, the
        hook is in the default state, and if it is inserted in a container, the hook
        is not in the default state.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="intrusive.safe_hook.configuring"></a><a class="link" href="safe_hook.html#intrusive.safe_hook.configuring" title="Configuring safe-mode assertions">Configuring safe-mode
      assertions</a>
</h3></div></div></div>
<p>
        By default, all safe-mode assertions raised by <span class="bold"><strong>Boost-Intrusive</strong></span>
        hooks and containers in are implemented using <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code>,
        which can be configured by the user. See <a href="http://www.boost.org/libs/utility/assert.html" target="_top">http://www.boost.org/libs/utility/assert.html</a>
        for more information about <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code>.
      </p>
<p>
        <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code> is globally
        configured, so the user might want to redefine intrusive safe-mode assertions
        without modifying the global <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code>.
        This can be achieved redefining the following macros:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            <code class="computeroutput"><span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DEFAULT_ASSERT</span></code>:
            This assertion will be used in insertion functions of the intrusive containers
            to check that the hook of the value to be inserted is default constructed.
          </li>
<li class="listitem">
            <code class="computeroutput"><span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DESTRUCTOR_ASSERT</span></code>:
            This assertion will be used in hooks' destructors to check that the hook
            is in a default state.
          </li>
</ul></div>
<p>
        If any of these macros is not redefined, the assertion will default to <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code>. If <code class="computeroutput"><span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DEFAULT_ASSERT</span></code>
        or <code class="computeroutput"><span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DESTRUCTOR_ASSERT</span></code>
        is defined and the programmer needs to include a file to configure that assertion,
        it can define <code class="computeroutput"><span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DESTRUCTOR_ASSERT_INCLUDE</span></code>
        or <code class="computeroutput"><span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DEFAULT_ASSERT_INCLUDE</span></code>
        with the name of the file to include:
      </p>
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DESTRUCTOR_ASSERT</span>          <span class="identifier">MYASSERT</span>
<span class="preprocessor">#define</span> <span class="identifier">BOOST_INTRUSIVE_SAFE_HOOK_DESTRUCTOR_ASSERT_INCLUDE</span> <span class="special">&lt;</span><span class="identifier">myassert</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span>
</pre>
</div>
</div>
<div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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